The invention relates to a monitoring apparatus in working machines having a working space into which body parts of an operator or other insertable parts must enter from at least one entry side for a period of time and in which working processes take place which endanger the body parts of the operator of the other insertable parts.
Conventional monitoring apparatus have at least one protective means arranged outside of the working space which is triggered, preferably unconsciously, by one or more body parts of the operator or by one or more insertable parts before entry into the working space takes place, and which on being triggered initiates, via an evaluation circuit, a stop signal or switch-on prevention signal for the machine.
The protective means can operate without contact and can for example, be formed as a light curtain (German application, Pub. No. 21 17 500) or also as a mechanical curtain with end switches (sliding door or the like). A further possibility consists in the person operating the working machine having to actuate a switch with both hands (two-handed switching) in order to initiate a machine cycle, so that it is impossible for the operator to encroach with one of the hands into the working space which becomes dangerous on switching on of the machine.
With regard to the machines one primarily thinks of large machines such as for example presses, pressure diecasting machines, blow molding machines and the like in which the requirement exists, in order to increase the economy, that the protective means which operates without contact should control the machine while being tied to the operating cycle thereof and to increase the safety of the plant.
With large tool installation spaces and low table height, the cycle-bound controlling of the machine using protective devices is, however, problematic because it is possible to walk within the tool installation spaces. The protective devices which are normally provided admittedly prevent starting of the machine or cause the stopping of the machine on being initiated. However, if the person leaves, for example, a protective device which operates without contact in the direction of the tool installation space within the predetermined cycle time, an undesired and dangerous machine start takes place. In the case of the presence of a two-handed switch, a person could initiate a machine start by orderly actuation of the two-handed switch and a second person could simultaneously enter into the dangerous working space. For this reason the controlling of large machines or large presses without additional protective means for monitoring the working space, in particular the tool installation space, is dangerous.